Materials Sciences and Applications, 2011, 2, 700-705
doi:10.4236/msa.2011.26096 Published Online June 2011 (
Copyright © 2011 SciRes. MSA
Equilibrium State of Anatase to Rutile
Transformation for Titanium Dioxide Film
Prepared by Ultrasonic Spray Pyrolysis Technique
Ghassem Kavei1,2, Auppatham Nakaruk2, Charles Chris Sorrell2
1Materials and Energy Research Centre, Tehran, Iran; 2School of Materials Science and Engineering University of New South Wales,
Sydney, Australia.
Received November 26th, 2010; revised December 25th, 2010; accepted May 9th, 2011.
Titanium dioxide thin films were deposited on (0001)
-quartz substrate by spray pyrolysis method. The method which
an aerosol of Titanium Butoxide, generated ultrasonically, was sprayed on the substrate at temperature of 400˚C, kept
at this temperature for periods of 3, 13, 19 and 39 hours. The developed films at a crystal phase correspond to the TiO2
anatase and rutile phases. Their surface roughness increased by annealing the samples at 600, 800 and 1000˚C. De-
posited film annealed at 1000˚C showed preferable orientation in (110) direction. The crystal evolution and crystallo-
graphic properties of this material was studied by Lotgering method, X-ray Diffraction (XRD) and Scanning Electron
Microscopy (SEM). The study revealed that the deposition process was nearly close to the classical Chemical Vapour
Deposition (CVD) technique that is generally employed to produce films with smooth surface and good crystalline
properties with a thickness of about 1 µm, as measured by Focused Ion Beam.
Keywords: Titanium Dioxide, Ultrasonic Spray Pyrolysis, Annealing Treatment, Phase Transformation, Focused Ion
Beam (FIB)
1. Introduction
In the past decade, considerable efforts were made to
synthesize self-cleaning materials, especially titanium
dioxide (TiO2 or titania). Basically, for self-cleaning ap-
plication, titania can be used in various forms such as
powder, [1] thin film [2-4] and thick films [5]. However,
thin and thick films are most commonly used due to their
flexible and applicable properties. Furthermore, titania
film can be employed as gas sensors [6] purifier of envi-
ronmental pollutants [7], photovoltaics and photocataly-
sis [8-10]. Therefore, plenty of literature reviews had
paid attention to thin or thick film coating methods such
as magnetron sputtering [11], Pulsed Laser Deposition
(PLD) [12], Chemical Vapour Deposition (CVD) [13],
sol-gel [6], gel oxidation [14], screen printing [15], an-
odic oxidation [16], and electrophoretic deposition [17].
Titanium oxide films are prepared by an ultrasonic nebu-
lization and pyrolysis technique developed by [18,19].
For self-cleaning applications, a titania film with small
band gap and large surface area (small grain size) is re-
quired. However, it is known that anatase phase will pro-
vide small grain size, but the band gap of the product is
greater than that of rutile. On the other hand, rutile phase
has smaller band gap but the resultant grains are larger
compared to anatase. Having this point in mind, one can
conclude that an intermediate phase between anatase and
rutile probably benefits from both small band gap and
moderate grain size and is advantageous for self-cleaning
It is well known that titanium dioxide consists of three
phases: brookite, anatase, and rutile [20]. Generally,
anatase will transform into rutile at ~600˚C, [21]. How-
ever, in thin film, the anatase temperature transformation
to rutile can rise up to 900˚C [22].
This study has been designed to confirm the formation
of a film with mixed phase of anatase and rutile struc-
tures at 400˚C. This was verified by inspecting the varia-
tion of effective parameters (such as time, substrate and
annealing temperature) on the samples.
2. Methodology
Ultrasonic spray pyrolysis was used to provide fully-
Equilibrium State of Anatase to Rutile Transformation for Titanium Dioxide 701
Film Prepared by Ultrasonic Spray Pyrolysis Technique
dense anatase and rutile thin films. The precursor mate-
rial (A starting solution) was prepared from titanium Bu-
toxide ([Ti(OCH2CH2CH2CH3)4], Reagent Grade 97 wt%,
Sigma-Aldrich) dissolved in methanol (Reagent Plus
99 wt%, Sigma-Aldrich) at a titanium concentration of
0.5 M. The aerosol as a mist was produced by means of a
generic ultrasonic generator of 1.7 MHz frequency. Com-
pressed air at pressure of 1.3 atm was admitted through a
shape tube ( shape, 12 cm in diameter) to align mist
molecules and direct molecules toward substrate. This
causes the molecules to be deposited uniformly on the
substrate. The substrate was (0001)
-quartz (1 × 20 × 20
mm) heated at a constant temperature up to 400˚C for 3 -
34 hours during the deposition process using a com-
mercial hotplate (SEM heater equipped with thermo-
digital controller). Deposited TiO2 films were annealed
in air at 600˚C, 800˚C, and 1000˚C for 7 h, at a heating
rate of 5˚C per minute, followed by a natural cooling
process overnight.
TiO2 films were characterised by the following tech-
niques: 1) Mineralogy and phase analysis of the films
was examined using laser Raman microspectroscopy
with a 514 nm Ar laser integrated with an optical micro-
scope (Renishaw in via), 2) the structures were defined
via glancing angle X-ray diffraction (GAXRD, angle of
incidence 1˚, penetration depth < 300 nm, Phillips X’pert
Materials Research Diffraction), and standard X-ray
powder diffraction (XRD, 20˚ - 80˚ 2θ, speed 0.02˚ 2θ/s,
step 0.01˚ 2θ, scans done in situ, Phillips X’pert Multi-
purpose X-ray Diffraction System) (MPD-Shurr) with 45
kV and 40 mA cathode voltage and current, respectively.
As a result, CuKα line radiation (λ = 1.5405 Å) was ob-
tained. 3) Surface morphology was evaluated by Field
Emission Scanning Electron Microscopy (FESEM) using
Hitachi (S4500X) model. 4) Film thickness was deter-
mined using single-beam focused ion beam (FIB) milling
(FEI XP200). In this system, a voltage of 30 kV was ap-
plied between the sample and probe, leading to a current
of 64 pA. Gallium ions (Ga3+) were used to erode a
square hole in the film and an image of the cross-section
of the layers was viewed at an angle of 45˚. To perform
SEM and FIB measurements, samples were coated with
~20 nm thick gold (Au) layer using sputtering technique.
3. Results and Discussion
Figure 1 show XRD patterns of titania films deposited
on the substrate. Table 1 also summarises the list of
peaks from XRD data. It can be seen that as-deposited
film at 400˚C consists of anatase and rutile phases of tita-
nium dioxide. There is a strong peak of anatase at (101)
plan with 2θ = 25.50˚ and a small peak of rutile at (110)
with 2θ = 27.58˚. After annealing at 600˚C and 800˚C for
7 h, the XRD patterns suggested that the rutile phase was
dominated. At annealing temperature of 1000˚C, anatase
was totally transformed into rutile.
Roughly speaking, anatase phase transformation into
rutile occurs at ~600˚C in titania powder [21]. Transfor-
mation temperature rises up to ~900˚C in the case of tita-
nia film [22]. Figure 2 shows XRD pattern of samples
being deposited in the substrate at 400˚C with various
durations, 3 - 24 hours. As depicted in this figure, the
patterns of TiO2 films are similar and contain anatase
phase. This implies that the nature of rutile phase formed
on as-deposited film does not change with temperature
du- ration. If a fixed substrate temperature had any direct
effect on the phase transformation of the TiO2 film, the
rutile phase would elevate after the long duration that the
films had been kept at a defined temperature (here is
400˚C) (see Figure 2). Therefore, the possible reason for
development of rutile phase in as-deposited film might
be a kinetic energy in TiO2 film for phase stabilisation at
particular temperature. In other words, the structural
transformation is greatly designated for an annealing
temperature and is almost independent of annealing du-
ration; a period which is not definitely longer than 7
hours as far as titania is concerned (see Figure 1).
Figure 3 shows the surface morphology of TiO2 films
at different annealing temperatures. Comparing the im-
ages of as-deposited film and annealed film at 600˚C
revealed that the film contained anatase phase (with
small grain size ~100 nm) and rutile phase (with large
grain size ~500 nm).
Annealing temperature increment densifies rutile phase.
These results confirmed by XRD patterns depicted in
Figure 1 in which the as-deposited film and annealed
film at 600˚C consisted of both anatase and rutile phases.
After annealing at 800˚C for 7 h, the surface morphology
showed that rutile phase is dominant. When annealed at
1000˚C, the film contained no anatase, implying that
anatase had completely turned into rutile with the aver-
age grain size of ~500 nm.
Since annealing process does not affect the film thick-
ness, as reported by, [23] the FIB photograph of the
as-deposited film in Figure 4 represents the thickness of
all TiO2 films. As illustrated in the figure, thickness of
as-deposited film was constantly ~1 m. Furthermore,
the grain size of anatase-rutile intermediate phase can be
seen in FIB image. More detailed analysis for the ex-
perimental results was studied, and basic mechanisms are
given for anatase to routile transformation analysis [19].
4. Conclusions
TiO2 thin films with smooth surface and crystalline
structure were obtained by pyrolysing an ultrasonically
Copyright © 2011 SciRes. MSA
Equilibrium State of Anatase to Rutile Transformation for Titanium Dioxide
Film Prepared by Ultrasonic Spray Pyrolysis Technique
Copyright © 2011 SciRes. MSA
Figure 1. XRD patterns of titania films prepared by ultrasonic spray pyrolysis at 400˚C for 3 h, and annealed at temperature
range of 600˚C to 1000˚C for 7 h.
2θ (degree)
Figure 2. XRD patterns of the film after deposition on the substrate at 400˚C for three hours the temperature of substrate
was kept at 400˚C for stabilization of the coated compounds with various durations (modified and raw spectra), (a) flattened;
(b) as recorded.
Equilibrium State of Anatase to Rutile Transformation for Titanium Dioxide 703
Film Prepared by Ultrasonic Spray Pyrolysis Technique
Table 1. Comparison between experimental (Film) and reported (Powder) 2θ peak positions from X-ray diffraction data for
anatase and rutile.
Polymorph Plane None 600˚C 800˚C 1000˚C Literature Reference
(101) 25.50 25.52 25.50 25.31
(004) 38.02 37.79
(200) 48.38 48.40 48.05
(105) 54.20 54.21 53.89
(211) 55.34 55.42 55.07
(204) 62.69
(220) 70.30
(215) 75.05
(110) 27.58 27.63 27.57 27.57 27.43
(101) 36.31 36.23 36.23 36.08
(200) 39.41 39.42 39.19
(111) 41.48 41.38 41.41 41.24
(210) 44.25 44.27 44.21 44.04
(211) 54.54 54.46 54.46 54.32
(220) 56.82 56.80 56.82 56.62
(310) 64.29 64.04
(301) 68.25 68.99
(112) 70.03 69.79
As-deposited at 400˚C Annealed at 600˚C
Annealed at 800˚C Annealed at 1000˚C
3 μm
Figure 3. SEM images of the TiO2 films surface showing morphology of the surfaces at different annealing temperatures.
Copyright © 2011 SciRes. MSA
Equilibrium State of Anatase to Rutile Transformation for Titanium Dioxide
Film Prepared by Ultrasonic Spray Pyrolysis Technique
Copyright © 2011 SciRes. MSA
Figure 4. Thickness of as-deposited film (measured to be ~1
m by FIB).
generated aerosol of Titanium (IV) Tert-Butoxide. Crys-
tal structure analysis, granular morphology and surface
roughness of as-deposited films and structure escalation
of once-annealed samples, revealed that the growth
process is closer to chemical vapour deposition rather
than to the typical splashing mechanisms of spray pyro-
lysis technique. Substrate temperature maintained at
400˚C. At higher temperatures, evolution of rutile phase
was significant. The developed surface showed different
magnitudes of the rutile phase intensity depending on
annealing temperatures. A crystalline phase of out-
standing transition to rutile was occurred when samples
were annealed at 1000˚C.
5. Acknowledgements
The first author thanks the Ministry of Science, Research
& Technology of Iran for giving him the chance to sab-
batical leave. Also, the authors are grateful for the finan-
cial support of Austral Brick Co. Pty. Ltd., which al-
lowed these and other researches in this category to be
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